1. Field
The present invention relates to a mobile telecommunication of third generation, and more particularly to a method for transmitting a transport format combination indicator (TFCI) inserted to each time slot of a radio frame in a mobile telecommunication system using a W-CDMA standard.
2. Background
Generally, a Third Generation Partnership Project (3GPP) group describes a definition of a physical channel of an upward link and a downward link of Radio Access Network (RAN). Here, a Dedicated Physical Channel (DPCH) comprises three-layer structure of super frames, radio frames and time slots. FIGS. 1 and 2 show two data structures of the DPCH. The first type is a Dedicated Physical Data Channel (DPDCH) for transferring dedicated data, and the second type is a Dedicated Control Channel (DPCCH) for transferring a control information.
FIG. 1 shows a data structure of an upward link DPCH according to the standard of 3GPP RAN, while FIG. 2 shows a data structure of a downward link DPCH. In FIGS. 1 and 2, the DPCCH includes a TFCI field in each time slot constituting a radio frame. In other words, information on a transmission format, i.e. TFCI, is coded and inserted into each radio frame.
The coding of the TFCI bits according to the 3GPP standard will next be explained.
The number of TFCI bits is variable from a minimum of 1 bit to a maximum of 10 bits, and the number of bits is determined from the point in time when a call starts through a signal processing of an upper layer. Different coding methods are applicable to the TFCI depending upon the number of bits. When the number of TFCI bits is less than 6, a bi-orthogonal coding or a first Reed-Muller coding is applicable. When the number of the TFCI bits is greater than 7, a second Reed-Muller coding is applicable. According to the 3GPP standard, the coded TFCI undergoes a puncturing to generate a code word of 30 bit length.
For example, when the number of TFCI bits, determined by upper layer signaling, is less than 6, a TFCI code word is output through a bi-orthogonal coding. Here, a (32, 6) coding is applicable to the bi-orthogonal coding. For that purpose, if the TFCI consists of less than 6 bits, a padding procedure is first executed to supplement the deficient bit value with “0” from the Most Significant Bit (MSB). Thereafter, the TFCI code word is inserted into each time slot of a radio frame by two bits. However, the entire length is restricted to be 30 bits. Thus, the TFCI code word of 32 bits, which has been bi-orthogonal coded, is punctured by 2 bits and inserted into each time slot.
In another example, when the number of TFCI bits determined by upper layer signaling not more than 10 bits, a TFCI code word is output through a second Reed-Muller coding. Here, a (32, 10) coding is applicable to the second Reed-Muller coding. For that purpose, if the TFCI bits are less than 10, a padding procedure is first executed to supplement the deficient bits with “0” from the MSB. The Reed-Muller coded TFCI code word is referred to as a sub-code. Accordingly, the sub-code is punctured by 2 bits to also generate a TFCI code word of 30 bit length. FIG. 3 is a block diagram illustrating a channel coding process.
The code word of 30 bit length generated as described above is divided into fifteen 2-bits and inserted into each time slot for transfer. FIG. 4 is a diagram showing a typical insertion of the coded TFCI code word into each time slot.
Also, FIG. 5 is a diagram illustrating an encoding structure for generating a (32, 10) TFCI code word according to the conventional second Reed-Muller coding. Referring to FIG. 5, the TFCI bits, variable from 1 to 10 bits are input to an encoder. The input data bit is lineally combined with 10 basis sequences. Namely, the basis sequences (32 element vectors) used for the linear combination comprises of a uniform code, in which all bit values are “1”; five orthogonal variable spreading factor codes represented by {C32, 1, C32, 2, C32, 4, C32, 8, C32, 16} as shown in Table 1; and four mask codes represented by {Mask1, Mask2, Mask3, Mask4} as shown in Table 2. In the conventional second Reed-Muller coding, the four mask codes are used to increase the number of code word by 16 times.
TABLE 1C32, 10000 0000 0000 0000 1111 1111 1111 1111C32, 20000 0000 1111 1111 0000 0000 1111 1111C32, 40000 1111 0000 1111 0000 1111 0000 1111C32, 80011 0011 0011 0011 0011 0011 0011 0011C32, 160101 0101 0101 0101 0101 0101 0101 0101
TABLE 2Mask10010 1000 0110 0011 1111 0000 0111 0111Mask20000 0001 1100 1101 0110 1101 1100 0111Mask30000 1010 1111 1001 0001 1011 0010 1011Mask40001 1100 0011 0111 0010 1111 0101 0001
Table 3 below shows the prior basis sequences, in which Mi,0 is the uniform code; Mi,1˜Mi,5 respectively corresponds to C32,1, C32,2. C32,4, C32,8, and C32,16; and Mi,6˜Mi,9 respectively corresponds to Mask1˜Mask4.
TABLE 3iMi,0Mi,1Mi,2Mi,3Mi,4Mi,5Mi,6Mi,7Mi,8Mi,901000000000110000100002100010100031000110001410010010115100101000161001100010710011101008101000011091010011110101010101011111010110011121011000110131011010101141011101001151011111111161100001000171100011100181100101101191100111010201101000111211101010101221101100011231101110111241110000100251110011101261110101010271110111001281111000010291111011100301111101110311111111111
The TFCI bits are lineally combined with the basis sequences described above and can be expressed by Equation 1, in which a0 represents the Least Significant Bit (LSB), while an−1 represents the MSB.an−1,an−2, . . . , a1, a0(n#10)  [Equation 1]
A TFCI code word of 30 bit length is subsequently output by puncturing the first and the 17th bits from the (32, 10) sub-code generated by the linear combination. The output TFCI code word of 30 bit length can be expressed by Equation 2:b0,b1,b2 . . . , b28, b29  [Equation 2]
Namely, the TFCI bits are input as expressed by Equation 1 are encoded by Equation 3 below to output the TFCI code word as expressed by Equation 2:bi=Σ(an×Mi,n)mod 2 (from n=0 to n=9, where i=0, 2, . . . , 31)  [Equation 3]
However, the TFCI encoding according to the technology in the related art as described above poses the following problems. First, the pattern of the TFCI bits input for encoding are improper because of the padding procedure necessary when the TFCI bits are input for coding. Particularly, when the TFCI bits for coding is less than 10, a padding procedure is typically executed to supplement the deficient bit values with “0” from the MSB. Therefore, a complex decoding procedure is necessary to decode the encoded and transmitted TFCI code words at a receiving party. Namely, a bi-orthogonal coding is necessary even when the input TFCI bits is less than 6. Thus, the receiving party needs to perform a priority check to confirm from which set the OVSF code, used for the encoding, has been selected between two OVSF code sets which are in binary complement relations. As a result, additional process and hardware are required.
Also, when two bits are punctured to generate a (30, 10) TFCI code word, inserted and transmitted to the actual TFCI field from the (32, 10) code word, a minimum hamming distance loss is up to 2 at maximum. Furthermore, although not explained above, one bit is punctured in a (16, 5) code word to generate a (15, 5) TFCI code word. In such case, a minimum hamming distance loss also occurs.